The present invention is directed to implantable medical devices and their use in monitoring physiological parameters within a patient's body. More particularly, the invention provides a high stability fast start-up oscillator for implantable medical devices. The oscillator is maintained in a first current mode using a low current and switched to a second current mode utilizing a higher current. The transition between current modes provides for a reduced startup time without consuming significantly more power. However, it would be recognized that the invention has a much broader range of applicability.
The use of implantable medical devices has become increasingly commonplace as an effective method of monitoring the state and condition of a living body. An implantable medical device can be implanted within a human or an animal to monitor physiological parameters about the patient's wellbeing. By being implanted directly within the body, implantable medical devices can provide continuous monitoring of the patient's condition without requiring continuous onsite care by a caregiver or a physician. Implantable medical devices can also provide therapy within the body to change or improve the patient's physical state based on the physiological parameters received from sensors or the like. Implantable devices have been used to help treat a variety of physical disorders, such as heart disease, deafness, and diabetes with a large degree of success.
As implantable medical devices are powered on and off, they can consume a significant amount of power during its operation. Implantable medical devices typically use an internal battery to power the device. The battery life or operational time that the implantable medical device can be used is an important factor in the design of the devices as a shortened battery life may require additional surgery to replace or recharge the device at an unwanted time for the patient. For this reason, it is desirable to reduce the power consumption within the implantable medical device to increase its time duration of operation.
Because of the power requirements needed to continuously sustain an implantable medical device, the implantable medical device may use a sleep state where the device is kept in a low-current usage state. The implantable medical device periodically looks or “sniffs” for a wake-up signal from an external device. Upon receiving the wake-up signal, the implantable medical device can be powered on to normal operation which utilizes significantly more current than during the sleep state. Alternatively, a duty cycle mode can be used by an implantable medical device to achieve lower power consumption, where the device is turned on during operation for a short time period and turned off following operation. Power savings can be achieved by duty cycling in that the implantable device is not continuously on.
One example of a device that can be included within an implantable medical device is a resonator oscillator that can be used for wireless communications. For example, resonator oscillators often utilize a quartz crystal as a resonance element to assist in starting up and shutting down the implant. The oscillator is maintained at an OFF state during the time when the implant is not operating to conserve power and is turned ON when the implant is in use. However, the transition from the OFF state to an on state can be quite long. For example, the start up time for a 10 MHz crystal, for instance, can be about 1-10 ms, which results in a slow duty cycle. The longer the start up time of the device, the higher duty cycle percentage that is needed to operate the implant.
A new oscillator and method of use could be developed which reduces the start up time of the device while not consuming significantly more current than before.